#define _CRT_SECURE_NO_WARNINGS 1
#include<iostream>
#include<vector>
#include<queue>
using namespace std;
class Solution {
    int dx[4] = { 0,0,1,-1 };
    int dy[4] = { 1,-1,0,0 };
    int m, n;
public:
    void solve(vector<vector<char>>& board) {
        m = board.size();
        n = board[0].size();
        for (int i = 0; i < n; i++)
        {
            if (board[0][i] == 'O')
            {
                bfs(board, 0, i);
            }
            if (board[m - 1][i] == 'O')
            {
                bfs(board, m - 1, i);
            }
        }
        for (int i = 0; i < m; i++)
        {
            if (board[i][0] == 'O')
            {
                bfs(board, i, 0);
            }
            if (board[i][n - 1] == 'O')
            {
                bfs(board, i, n - 1);
            }
        }
        for (int i = 0; i < m; i++)
        {
            for (int j = 0; j < n; j++)
            {
                if (board[i][j] == 'O')
                {
                    board[i][j] = 'X';
                }
                else if (board[i][j] == '.')
                {
                    board[i][j] = 'O';
                }
            }
        }
    }
    void bfs(vector<vector<char>>& board, int i, int j)
    {
        queue<pair<int, int>> qw;
        board[i][j] = '.';
        qw.push({ i,j });
        while (qw.size())
        {
            auto [a, b] = qw.front();
            qw.pop();
            for (int k = 0; k < 4; k++)
            {
                int x = a + dx[k];
                int y = b + dy[k];
                if (x >= 0 && x < m && y >= 0 && y < n && board[x][y] == 'O')
                {
                    qw.push({ x,y });
                    board[x][y] = '.';
                }
            }
        }
    }
};